what is the maximum amount that an employee can shelter into a 401 (k) plan?

What is a personal allowance? what was the amount of personal allowance for 2012?

Orrin D'Amato, Single, participates in his firms pension retirement plan. This year, his modified adjusted gross income will be about $70,000. How much of his compensation may D'Amato contribute to an IRA this year(2012) without paying federal income taxes on the contribution?

Under what conditions may employees be exempt from the withholding of federal income taxes during 2012?